مجله مهندسی زیر ساخت های حمل و نقل
سال دوم شماره 4 (پیاپی 8، زمستان 1395)

Asphalt concrete is a self-healing material which can repair damages automatically when it is exposed to rest periods. Healing of an asphalt concrete is the recovery of its stiffness and strength due to closure of the internal cracks. Nevertheless¡ healing rate in ambient temperature¡ especially at low temperature¡ is slow and traffic circulation can''t be closed during reaching sufficient healing. Furthermore¡ self-healing of asphalt concrete is much dependent on temperature and pavement healing will increase at high temperatures. In this research¡ microwave heating was used in order to increase asphalt concrete self-healing capacity through temperature increase. Varying amounts of carbon fiber and steel wool were added to the asphalt mixture to increase thermal efficiency by microwave heating. According to the results of type and optimum wool percent test¡ it was observed that samples with carbon fibers have better efficiency compared to other mixtures with steel wool. Also¡ optimum carbon fiber percent was obtained as 0.2% of mixture''s total mass. Moreover¡ in order to investigate self-healing process in asphalt mixture¡ fatigue life test¡ Cantabro durability test and indirect tensile test were conducted on the samples. Test results showed that heating causes an increase in healing rate of fatigue life and tensile strength and failure samples can recover part of their lost properties. Also¡ healing rate increases with temperature rise¡ as well. Also¡ it was revealed that heating should not be applied very late. Cantabro durability test results showed if heating is applied between the rotations¡ aggregate separation will be reduced because of increasing cohesion between bitumen and aggregates.

Due to sustainable development, environmental concerns caused by air pollution, expansion of development projects, and limitations of mineral aggregates, reduction of construction temperature of asphalt mixtures and use of secondary materials as substitute for aggregate materials is inevitable. In this research, long-term performance of warm asphalt mixtures containing steel slag was investigated. Limestone aggregates and steel slag of Electric Arc Furnace (EAF) were the main materials and Sasobit was used as an additive in manufacturing warm asphalt mixtures. Using 1.5% Sasobit, with respect to bitumen’s weight, decreased temperature of the asphalt mixtures by 20 °C. In order to simulate short-term and long-term aging of asphalt samples, AASHTO R35 and AASHTO R30 standards were used. Sasobit was mixed with asphalt by conventional mixer and high-shear mixer. Traditional and SHRP tests conducted on mixtures indicated that Sasobit is insensitive to mixing conditions. Performance of asphalt samples was evaluated by Marshall stability test, resilient modulus test, indirect tensile strength test, moisture susceptibility test and dynamic creep test. Finally, quantitative growth of the results for each sample, with respect to hot calcareous asphalt mixture, was presented. In general, using slag as calcareous substitute caused higher aging of asphalt mixtures. Also, hot asphalt samples, as compared to warm asphalt mixtures, were more sensitive to aging. As warm asphalt mixtures containing EAF steel slag, with respect to other asphalt mixtures, have shown long-term and short-term performance, therefore, they are recommendable.

The vibrations applied to bridges during their normal operation conditions can be defined as ambient vibrations. These vibrations include the effects of traffic, wind and other low excitations imposed to the structure. Detection and evaluation of the location and dimensions of the damages are accounted as one of the most important stages for structural maintenance. These damages may often occur due to ignorance of standard clauses during structural design, neglecting proper construction regulations, high age of the structure and improper structural maintenance. Using a simple and classic method for damage detection in bridge piers can be significantly efficient. Nowadays, metaheuristic algorithms are widely used in structures. Although in this study, it is aimed to use only mathematical and classic methods of optimization, which imply better physical understanding, however in this paper, a new method based on inverse problem, is proposed to detect ambient damages in bridge piers. In this proposed method, firstly the damage percentage and its location are assumed based on a typical damage scenario. Then, assuming lack of sufficient vibration data, the variable (stiffness degradation percentage) is defined using optimization method and introducing objective function for axial flexural member of the bridge pier. Assuming linear damage up to spalling of the concrete, the errors at three modes using linear optimization simplex method are revealed 0.7, 0.1 and 1.45 percent (mostly three equations). The obtained results showed good agreement with the initial values. Also, results of an experiment are used to validate the models. Evaluation of the experimental and analytical results showed that the proposed method for damage detection of RC bridge piers can be precisely applied

Soil stabilization is an effective method employed in order to improve soil properties, using different stabilization agents. As well using fibers as reinforcement of weak soils which generally have no tension and low bearing capacity is a well-known method. This study has investigated simultaneously using of palm date fibers and cement in order to improve the key characteristics of a specific soil type in Qeshm island. Cement was used as the main soil stabilizer and palm date fibers were included in soil composite as a reinforcing elements. The palm fibers in date production have filament texture with special properties such as: low cost, plenitude in the region, durability, light weight, tension capacity and relative strength against deterioration. In this study, test specimens, with a fixed cement content (6%), were fabricated including different fiber content (%0.5 and %1.0). The specimens were cured 7 and 28 days and were immersed in water for four hours prior to indirect tensile strength (ITS) and unconfined compressive strength (UCS) tests. As well, CBR specimens were cured (7 and 28 days) and tested in both optimum water content and saturated conditions. Compaction tests results shows that increasing fiber content in soil result in decrease of maximum dry density and increase of optimum moisture content. ITS and UCS results shows the most improvement in tensile strength (almost %48) and compressive strength, for %0.5 fiber inclusion. CBR test results shows that CBR values has increased with increase in fiber content in the soil.

Design of technical buildings and urban infrastructures, like transportation systems, requires preliminary estimates of geotechnical parameters. Thus, it is very important to prepare detailed engineering properties of soil deposits in different areas based on geotechnical investigations. This study aims to evaluate soil properties followed by a geotechnical database for Semnan City, Iran. For this purpose, wide information was collected from 110 geotechnical boreholes. In addition to the statistical analysis of the collected tests results, physical and mechanical soil parameters of Semnan City were zoned using kriging statistical interpolation method by ArcGIS software. Preparation of such basic information, while having the ability to be completed and updated, can provide the conditions for better estimation of geotechnical parameters in the studied region. The internal friction angle, cohesion, density and soil moisture content parameters were zoned using statistical interpolation method. Finally, based on the carried out zonation, ground conditions in different areas of the studied region were described

The routes exposed to snow and rain, with a chance of freezing, need de-icing due to the possibility of exploitation of the route and protection against structural damage. Lack of maintenance and de-icing leads to swelling of the surface, contractile cracks, expansion of existing cracks, separation of the pavement layers and in some cases separation of the grains. Calcium chloride, magnesium chloride, sodium chloride and urea can be used as de-icing and liquid anti-icing materials. In using the above materials, in addition to the ecological and economical aspects, damages caused to asphalt surface due to the close contact with these materials should be evaluated. The aim of this study was laboratory investigation of the effect of using the above materials on asphaltic-mixture resistance. For this purpose, the prepared samples were cured according to AASHTO T283 and tested for Marshal stability, tensile strength and resilient modulus. Results indicated that deicing with calcium chloride solution in Marshal stability test, calcium chloride and urea solution in tensile strength test, and urea in resilient modulus test has the lowest negative effect. Also, since the mixture is in close contact with pure water and freeze-thaw cycle, it has the highest negative effct on the laboratory samples and this approves and emphasizes the need for proper maintenance and use of anti-icing and de-icing materials. Therefore, considering the negative ecological effects, effective temperature, price of the materials and results of this research, in areas where the temperature is 0 to -10, or -10 to -20 or lower than -20 °C, then urea, magnesium chloride and calcium chloride can be used as de-icing material, respectively, to have the lowest damages to asphalt pavement.

Nowadays, the use of bridges with wall-piers is common in urban highways and freeways. The limitations of space, particularly in urban constructions, and the landscape architectural aspects are the main reasons that this system is being interesting. These bridges are structurally designed in various types of single-wall and multi-wall piers. Nonlinear performance of piers was investigated using pier by pier method as well as the pushover analysis by SAP2000 software. Considering one length of wall required for seismic design, four cases including pier with four, three, two, and one-wall were studied in this analysis. The effects of foundation and soil-foundation interaction were considered in all the analyses. The results demonstrated that efficiency of pier is being reduced to about 33% by reducing the number of walls from four to one-wall in the pier, regardless of the constant strength. Thus, it is recommended to apply multi-wall pier system rather than single-wall pier in bridges.